I. Field of the Invention
The present invention relates to a filtration system for use in storm drain collection boxes, and, more particularly, to such a system in which a sock or sleeve made of filtration fabric is supported by a helical frame with one open end of the frame being attached to and suspended from a ceiling of the collection box and an opposite open end of the frame being attached to an exit sidewall of the collection box in alignment with an outlet opening in the box.
II. Description of the Related Art
The handling of storm water run-off is an ongoing problem in many communities. Residential and commercial development results in streets, roadways and parking lots, houses and other buildings replacing soil, tree and plant life. This means that the natural moisture absorbing properties of the soil and plants are taken away and replaced by these moisture impervious structures. Thus, when rain and snowfall do occur, the run-off of water from these developed areas is much faster and occurs with greater volume and erosive tendencies than previously.
This increased run-off in developed areas is typically handled by the installation of below ground storm water drainage pipe systems which collect the water via a series of storm drain collection boxes. The collection boxes are typically concrete receptacles with curb drainage inlets positioned at collection points where water is funneled via roadways, parking lots and curbs. Typically these storm water drainage systems output collected water directly into downstream waterways and lakes with no water treatment or filtration.
Ever increasing concern for the environment and more stringent government requirements on the passing of silt, sediment and solid materials into waterways have created problems in the handling of storm water. In many cities and states new environmental regulations require developers to utilize "Best Management Practices" to decrease or eliminate the introduction of silt, sediments, solid materials and other pollutants into the waterways. This presents a major problem for developers who must use existing techniques for handling storm water run-off. As a final collection point prior to release from a development site, storm drain collection boxes offer an opportunity to process and improve storm water quality before it is discharged into the waterways. The pursuit of Best Management Practices requires that new filtration systems must be developed to adapt existing storm water collection boxes to the new regulations.
A common method of attempting to deal with filtration in collection boxes are a class of filters that are commonly referred to as "throat filters". These are positioned at street level at the inlet mouth of the collection boxes. These throat filters can be simple and economical, e.g. sand bags, but present a number of problems. Throat filters are typically placed over or around the collection box opening and function primarily as a sediment and solid materials barrier. They are in clear view i.e. on the pavement surface and are thus often removed by property owners for aesthetic reasons. When functioning properly, throat filters offer poor filtration properties and, by design, block the entrance of storm water into the collection box. Thus storm water either bypasses the collection box or begins to pool on the adjacent pavement resulting in localized flooding. This causes pedestrian and vehicle hazards during a heavy rain. The hazard continues after the storm water drains or evaporates away when it leaves behind a layer of deposited sediment and solid materials (cups, cans, papers, etc.) around the throat filters, i.e. on the pavement. Finally, throat filters require considerable maintenance, particularly immediately after a storm and are typically not anchored, which means that they can be lifted by hydraulic pressure during heavy rains, thus allowing unfiltered water to enter the collection box under the lifted filter.
One attempt to fit existing collection boxes with an internal filtration system is found in U.S. Pat. No. 5,405,539 to Thomas Schneider. In the Schneider system, a filter frame is inserted into the collection box in pieces and assembled therein. The frame includes a telescoping bed portion which is positioned adjacent to the front of the collection box with a frame back portion abutting the bed portion such that, when assembled, the bed and back portions resemble "a bench-type seat". A sheet of filter material is then laid over the bed and back portions. The bed portion is supported off of the floor of the collection box by a series of legs and is urged in position against the front of the box by pneumatic cylinders. Water entering the collection box, as modified by the Schneider filter system, flows onto the bed portion and through the sheet of filter material, which filters out dirt, sediment and solid materials with the filtered water then flowing out of the collection box outlet. Should the filter become clogged or when water inflow exceeds the capacity of the filter, unfiltered water flows over the back portion and out of the collection box outlet.
A number of problems are also presented by the Schneider system. The capacity of the Schneider system is very limited since only the bed portion, and the back portion in heavy rains, is available for filtration area and, thus, the total square footage of filtration area is relatively small. This means that overflow of non-filtered water may occur in fairly low intensity rains. The elevation of the bed portion off of the floor of the collection box by the legs and the positioning of the bed portion in front of the box makes it visible and accessible from the box inlet mouth. This position and the horizontal orientation of the bed portion mean that the capacity of the Schneider filter system for holding trash and debris is fairly limited and also makes collected sediment and debris visible from the box mouth, presenting an unsightly condition, and, when the filter is clogged, can result in pooling of stagnant water on the clogged horizontal bed surface. Finally, the Schneider filter requires frequent maintenance as well, preferably after each storm event, and the occupation of the majority of the collection box by the Schneider filter frame means that it is difficult to get a person inside the box to change the filter material and remove solid materials.
It is clear then, that a need exists for an effective storm water collection box filtration system which is usable with existing collection box designs. Such a filtration system should preferably be economical, easily and quickly installed, and should occupy a minimal volume of the collection box, thus making the bulk of the collection box itself available as a solid materials collector. The filtration system should preferably maintain the integrity of the engineered storm water system design and capacity as closely as possible and should require less maintenance than prior art systems but yet be simpler and easier to clean and maintain. Finally, the filtration system should be adaptable to virtually any size of collection box and storm water pipe outlet, which sizes vary considerably by locale and local design considerations.